A feeder reconfiguration in utility distribution systems has been an important aspect of distribution automation. The reconfiguration is used to avoid overloading of transformers and feeders resulting from load variations. In a distribution feeder, the load may vary with time and overshoot its rated thermal capacity during some heavy load period. The load variation also depends on the kind of load such as residential load, commercial or industrial load. In case of an overload, in order to keep the system reliable, a part of the load from the overloaded feeder should be transferred to an adjacent feeder that is relatively lightly loaded. Similarly main transformer overloading can be addressed by identifying the appropriate feeder causing the overload and transferring a part of load from that feeder load to an adjacent transformer which is lightly loaded. This redistribution of load among feeders and transformers makes the system more balanced and the risk of overloading is reduced thereby increasing the reliability of a system.
U.S. Pat. No. 6,654,216 provides a distributed monitoring and protection system for a distributed power network. The power network has a plurality of lines for transmitting electric power from a station with circuit breakers included in the lines. The distributed monitoring and protection system includes at least one monitoring unit coupled to at least one of the plurality of power lines for measuring electrical parameters of the power line; and at least one control unit communicating over a data network with the monitoring unit and receiving measured electrical parameters from the monitoring unit.
The protection system described monitors electrical parameters (e.g., current, voltage) in the system to their threshold values and causes tripping of circuit breakers when any electrical parameter overshoots its threshold value. The method described does not involve normalization of load over a variety of equipment by minimization of an objective function.
U.S. Pat. No. 5,734,586 pertains to large-scale, unbalanced, power-distribution networks for achieving steady state by the use of a loss formula, a voltage formula and a line-flow formula therefor. Also disclosed is an explicit formula for determining the variations in system losses, three-phase line flows and voltages, in terms of system and network data, with respect to variations in control devices, network components and connections. Applications of the explicit expression to real-time control of distribution systems are identified. The three-phase power flow and loss formulae are capable of coping with a great number of nodes, branches and laterals; multiphase, grounded or ungrounded loads; co-generators, multiphase shunt elements and transformers of any connections in general, large-scale, unbalanced distribution systems.
The system described does not involve normalization of load over a variety of equipment. Also, it is relatively complex, involving network flow programming techniques and an estimation of the effect of control steps before the actual implementation of control steps.
There are numerous publications dealing with reconfiguration but, except for a few publications, none of them explain on-line reconfiguration. The few publications had algorithms described in a complex way. Heuristic techniques have been proposed to attempt a near optimal solution in a short period. Other techniques include an approach in which the optimal configuration was achieved by opening the branches with lowest current in the optimal load flow solutions for the configuration with all switches closed. There are publications that propose a reconfiguration of the phase balancing using a fuzzy logic and a combinatorial optimization-based implementation step back to back. An input to the fuzzy step is the total load per phase of the feeders. An output of the fuzzy step is the load change values, with a negative value for load releasing and a positive value for load receiving. The output of the fuzzy step is the input to the load changing system. The load changing system uses combinatorial optimization techniques to translate the change values (kW) into a number of load points, and then selects specific load points. It also performs an inter-changing of the load points between the releasing and the receiving phases in an optimal fashion.
Index values used in Kashmen M. A., “Three-phase load balancing in distribution systems using index measurement technique”, International Journal of Electrical Power & Energy systems, January 2002, are the branch load balancing indices, and the disclosed system is not directed to control from a system perspective.
In the method described in the publication, network reconfiguration for load balancing is implemented by performing a search over different radial configurations created by considering branch-exchange type switches.
It would be desirable to have a system approach wherein a loading condition of the branches and the overall system, using indices suitable for the branches and an index value of the system, help achieve optimum load balancing. Such systems would be desirable to improve known systems and methods for management of an electrical power distribution system.